The first factor is (5^6)^3. Multiply the exponents 6 and 3 together, obtaining 5^18. Next, rewrite 25^3 as (5^2)^3, or 5^6. Finally, write 125^8 as (5^3)^8.
It would be 8. To solve, look at it like this: 8-b=(-2). I would then look at a number line or create one if your not to sure of yourself. 8-8=0, and then 0-2=-2. 2+8=10 (the numbers you subtracted). So the answer is 10.